In the last two decades there has been an increasing awareness of the need to assay for the presence of a large number of different types of analytes, as well as in many cases to be able to quantitate a particular analyte. During the 70's, a number of different chemistries were developed to avoid the need to use radioisotopes, where RIA was the primary technique for detecting a specific ligand or receptor. A wide variety of labels have been developed which would appear to have reached their ultimate degree of sensitivity in conjunction with the protocols and intrumentation that has been available. While much of the effort has been directed to developing intrumentation which can handle a large number of assays in a substantially automated manner, the market for low volume assays for a variety of different ligands has been increasingly expanding. The need for this market is to be able to perform an extended number of assays for different ligands in relatively low numbers for each ligand and with a minimum of technical competence. Therefore, in many cases, the protocol for the preparation of the sample should be simple and pretreating of the sample should be relatively routine.
To answer the increasing need for detection of ligands, there have been numerous developments to improve instrumentation in combination with particular chemistries. Thus, there are a number of available instruments which are reasonably sensitive, have a relatively low requirement of technical competence, and the newer instrumentation is less expensive than prior instrumentation. Nevertheless, for many aspects of the market, there still remains an important need for a simple, efficient and inexpensive device, which allows for the sensitive detection of low levels of ligands in a variety of media.